Wrought stainless steel



WROUGHT STAINLESS STEEL William C. Clarke, Jr., Baltimore, Md., assignor to Armco Steel Corporation, a corporation of Ohio No Drawing. Application May 19, 1954, Serial No. 431,010

7 Claims. (Cl. 148-31) My invention relates generally to precipitation-hardenable stainless steels, and, more particularly, it concerns forgings and other wrought products fabricated of such steels, particularly products which are not drastically reduced in the working.

An object of my invention is to provide stainless steels which can be readily forged of otherwise hot-worked into products which may be only lightly reduced and thereafter precipitation-hardened, all with a relatively few simple manipulative steps, in the practice of which the resulting final products display requisite strength and other physical qualities, and with substantially homogeneous composition throughout.

Another object is to produce precipitation-hardenable wrought metal products of the general type described which, even when of substantial dimensions and of light reduction, are uniformly sound and display homogeneous and continuous composition throughout their extent, with those inter-metallic compounds present being uniformly distributed therethrough, and which, in precipitationhardened condition, have desirable mechanical properties and are capable of being welded effectively, such welds being sound, uniform and without defect.

Yet another object is to produce precipitation-hardened stainless steel forged products of substantial dimensions of the general character described which may be but lightly reduced and yet with substantial freedom from segregates and other defects and blemishes.

Other objects and advantages will in part be obvious and in part more fully pointed out hereinafter, during the course of the following description.

My invention may be seen to reside, therefore, in the several procedural and manipulative steps, in the composition of ingredients, in the products forged or otherwise worked therefrom, and as well, in the combination and interrelation of each of the same with one ormore of the others, the scope of/the application of all of which is more fully set forth in the claims at the end of this specification.

Referring now to the practice of my invention, I find that a steel essentially consisting of chromium 15.5% to 17.5%, nickel 3.0% to 4.0%, copper within the approximate range of 2.5% to 3%, and remainder iron possesses an excellent combination of hot-working and precipitation-hardening properties. Satisfactory results are obtained with chromium 15.0% to 18.5%, nickel 2.8% to 5.6%, copper 2.00% to 3.00%, and remainder iron. In these steels the permissible range of copper is 1.00% to 3.00% It is my observation that the percentage of copper present in thealloy exercises remarkable control on the hot-working properties. Although I am by no means certain of this point, and offer it simply as a possible and tentative explanation of the phenomenon encountered,

'1 atent" 2,784,125 Patented Mar. 5, 1957 excess of the 3% figure which I consider critical, copper segregates frequently form due to the slow cooling rateof the ingot. When the product undergoing production is worked to small dimensions, that is in excess of say 75% reduction, the alloy is worked sufliciently so that the Sega regates are re-dissolved and homogeneity of composition is achieved. Substantially all of the copper passes into solution. But when the ingot is but lightly hot-worked, say less than 75% or even less than 50%, as by forging, rolling, drawing or the like, giving products of substantial dimensions, the effect of this working is not sufficient to dissipate segregates. And it is in the region of these copper-rich pools, as demonstrated by microscopic examination of the specimens investigated, that I find failure; there is no strength in the copper pools and the steel is inclined to tear. Regardless of 'basic reason, close control of the copper content of the alloy metal within the certain limits recited results in a product which admirably possesses the advantageous qualities which I seek.

In the production of my precipitation-hardenable stainless steel aluminum is frequently employed in the melt shortly before tapping. Usually aluminum is introduced as a de-oxidizer, some controlled small percentages of aluminum remaining in the metal after slag is dumped. I find that this aluminum cuts the solubility of the metal for copper. Since such aluminum does nototherwise play an essential part in my alloy steel, I find it best to keep the aluminum content as low as possible, consistent with its use as a de-oxidizer, this on the order of one pound per ton of steel in melting, giving a residual aluminum content not exceeding 0.20%..

And I find certain benefits are had, notablyslightly lower hardness in the annealed condition and somewhat improved weldability and greater soundness, by including columbium and/ or tantalum in total amount up to about 0.50%. With this addition the nickel content preferably is about 4.3%, the range being 3.9% to 4.8%. Without the addition, however, the nickel content preferably is approximately 3.5 the range being 3.0% to 4.0% as previously noted.

In undertaking to verify my conclusions by experimental tests, I prepared a number of heats in accordance with the following table:

TABLE I Analyses of precipitation-hardeningsteelswith progressive variations in the copper content Heat No. 0 Mn Or Ni Cu In the heats noted the chromium is abut 16%, the

In large ingots, where copper is in TABLE II Properties of steels of Table l Mechanical Properties in Precipitation-Hardened Condition Hot-working Copper Properties Heat No. Content, in Annealed Percent U. '1. S .2% E1. in 2" R. A., Rockwell Condition p. s. 1. Y. S. Percent Percent Har p. s. 1. ness 3. 98 187, 000 153, 000 10. 30. 0 C41 Poor-cracked in rolling. 3.50 188, 000 175, 000 10. 0 45. 0 C43 Do. 2. 98 188, 000 155, 000 10. 0 42. 0 C41 Good. 2. 56 188, 000 145, 000 10. 0 35. 0 041 Do. 3. 184, 500 161, 400 12.0 24. 9 C42. 0 Do. 2. 58 191, 700 166, 100 10. 0 26.0 041. 5 Do. 2. 16 182, 000 157, 300 8. 0 21. 3 C40. 5 Do. 1. 70 173, 600 145, 900 10. 0 23. 7 C39. 5 D0. 1. 09 174, 800 143, 400 13.0 32. 5 C39. 0 Do.

No'rn.-a, b, c, and :1 mechanical properties for .250 rods. properties for .505" erode.- Precipitation-hardening, and oil quench, by re-heating to 900 F. for 1 hour and air 0001.

Accordingly, specimens according to my investigation were provided, having copper content ranging from about 1.0% to about 4.0%. These were hot-forged. Samples were precipitation-hardened, following annealing at 1900 F. for one hour and oil quench, by re-heating to 900 F. for one hour and air cooling. These were then subjected to a variety of mechanical tests. The steels containing 3.50% and 3.98% copper respectively displayed cracking in hot-working. The steels analyzing no higher than 3.0% copper, however, failed to reveal any evidence of cracking.

Moreover, the steels with copper content ranging from about 2.5% to about-3.0% possessed nearly the same physical properties as did the higher copper content alloys, and yet provided satisfactory hot-working properties. The hot-working properties of materials ranging from 2.0%' to 2.5% copper likewise were satisfactory. At the same time their useful mechanical properties, while lower than those of the specimens of conventional copper content, nevertheless are within useful range.

Concerning improved welding qualities, I find that the steels containing 3.0% and 2.5% copper display no tendency to form toe cracks or underbead cracks in the base metal adjacent the weld. Entirely satisfactory Weld joints can now be made, with this controlled introduction of copper into the material, even in the more massive products involved in industrial application, either monolithic or fabricated in nature. Mechanical properties are highly desirable. Controlled dimensions with excellent mechanical properties in the final product can be achieved, through effective combination of first working in annealed condition, followed by precipitation-hardening through heat treatment. And the products thus produced, regardless of their dimensions, can be effectively welded with the production of tight, sound weld joints. Uniform and homogeneous composition exists throughout the cross-sectional area of such products, and this regardless of the region at which the cross-section is taken. Copperrich pools are characterized by their absence. This homogeneous composition is demonstrated by microscopic examination.

All of the aforementioned objectives in large measure are achieved by precipitation-hardenable steels wherein the important copper additive is preserved at a maximum of 3.0% and preferably between the range of 2.5% to 3.0%, although satisfactory results can be had with copper content as low as 1.0%. Aluminum is kept within controlled low traces. The forged products thus produced are entirely satisfactory, displaying, after precipitation hardening, the required mechanical properties, and this together with highly satisfactory properties, all without regard to the dimensional importance of the products undergoing fabrication and without regard to, the limited extent of the reduction had. Initial production costs are ,1] 51, and i mechanical following anneal at 1,900 1?. 1 hour,

low, as is true of subsequent manipulation and manufacturing costs.

All the forgoing, as well as many other highly satisfactory objects and advantages, attend the practice of my invention.

It is apparent that once the broad aspects of my invention are disclosed, many embodiments will readily suggest themselves to those skilled in the art, all falling within the scope of my disclosure. And as well, many modifications of the illustrated embodiments will likewise suggest themselves. Accordingly, I intend the foregoing disclosure to be considered as merely illustrative, and not by way of limitation.

I claim as my invention:

1. Hot-worked alloy steel products capable of precipitation-hardening, which hot-worked products display substantially uniform and homogeneous composition with copper-rich phase uniformly dispersed therethrough even in products reduced as lightly as 50%, said steel products essentially consisting of about 15.0% to 18.5% chromium, about 2.8% to 5.6% nickel, about 1.0% to about 3.0% copper, with aluminum but this not exceeding 0.20%, and remainder iron.

2. Hot-worked alloy steel products capable of being successfully precipitation-hardened, which hot-worked products display homogeneous composition throughout with copper-rich phase dispersed substantially uniformly therethrough even in products reduced as much as 50%, and essentially consisting of approximately 15.5% to 17.5% chromium, approximately 3.0% to 4.8% nickel, about 2.5% to about 3% copper, with columbium and tantalum together in amounts up to about 0.50%, and remainder iron.

3. Precipitation-hardened alloy steel hot-worked articles essentially analyzing approximately 16.5% chromium, 3.5% nickel, copper ranging from 1% to 3%, and remainder iron.

4. Precipitation-hardened alloy steel hot-worked articles essentially analyzing approximately 16.5 chromium, 4.3% nickel, copper ranging from 1% to 3%, with columbium and tantalum together in amounts up to about 0.50%, and remainder iron.

5. An article of manufacture hot-worked to final dimensions and then precipitation-hardened and capable of the production therein of sound, uniform welds, both in the weld itself and in the region of the base metal surrounding the weld and displaying desirable mechanical properties, the alloy metal essentially consisting of chromium approximately 16.5%, nickel 3.0% to 4.0%, copper 1% to 3%, and remainder iron.

6. A welded hot-worked article of precipitation-hardened stainless steel essentially consisting of 15.0% to 18.5% chromium, 2.8% to 5.6% nickel, 1.0% to 3.0% copper, and remainder iron.

2,784,125 5 6 7. A Welded forging of precipitation-hardened stain- References Cited in the file of this patent less steel essentially consisting of 16.5% chromium, 4.3% UNITED STATES PATENTS nickel, copper ranging from 1% to 3%, with columbium and tantalum together in amounts up to about 0.50%, 2482096 Clarka Sept- 1949 and remainder iron. 5 FOREIGN PATENTS 49,211 France Sept. 6, 1938 Addition to 803.361 

1. HOT-WORKED ALLOY STEEL PRODUCTS CAPABLE OF PRECIPITATION-HARDENING, WHICH HOT-WORKED PRODUCTS DISPLAY SUBSTANTIALLY UNIFORM AND HOMOGENEOUS COMPOSITION WITH COPPER-RICH PHASE UNIFORMLY DISPERSED THERETHROUGH EVEN IN PRODUCTS REDUCED AS LIGHTLY AS 50%, SAID STEEL PRODUCTS ESSENTIALLY CONSISTING OF ABOUT 15.0% TO 18.5% CHROMIUM, ABOUT 2.8% TO 5.6% NICKEL, ABOUT 1.0% TO ABOUT 3.0% COPPER, WITH ALUMINUM BUT THIS NOT EXCEEDING 0.20%, AND REMAINDER IRON. 